Tension measuring device



June 29, 1948. J. D. CAMPBELL 2,444,245

TEN-SION MEASURING DEVICE I l Filed May '1, 1946 3 Sheets-Sheet 1 James D. Campbel I,

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@Q 1b.@ .P n omhw im JMA .me m H @mf June 29, 1948. J. DQ CAMPBELL A TENSION MEASURING DEVICE .3 Sheets-Sheet 3 Filed May ll 1946 \||l, PD. r @TWO tat HC t ,u A ns @by Patented June 29g, 1948 TENSION MaAsUarNG DEVICE y James n. csmbeu, Schenectady. N. Y., signor to General Electric New York Company, a corporation oi' Application May 1, 1946, Serial No. 666,482 s claims. (c1. 734144) This invention relates to devices for measuring tension; more particularly to devices for measuring tension in a length of material extending between two work performing devices, and it has for an object the provision of a simple, reliable, and inexpensive device of this character.

Still morel specifically the invention relates to devices for use in combination with vloopers for the measurement of tension in a strip of material which is passing over the looper.

In carrying the invention into effect in one form thereof, a looper is provided which has a roller that is carried on a pivoted supporting arm and is` disposed to bear against a strip of material which extends between two work performing devices. Means are provided for applying a force to rotate the arm through an angle to deflect the strip from the line between the two work devices. Means are provided for producing a voltage proportional to the sine of the angle through which the arm is rotated and a second voltage which is proportional to the force of the roller against the strip. The ratio of these two voltages which is proportional to the tension of the strip is measured by means of an electrical ratio meter which is calibrated in units of tension.

In illustrating the invention in one form thereof it is shown as applied to the measurement of tension in a steel strip which is being passed through a rolling mill.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawings of which Fig. lis a slmple, diagrammatic sketch of an embodiment of the invention, Figs. 2 and 4, are simple, diagrammatic sketches of modications, and Fig. 3 is a sketch of a detail.

Referring now to the drawing, a length of material I, such as a strip of steel, is being passed in the direction of the arrows through successive stands 2 and 3 oi'. a rolling mill. Situated 'between the two stands is a looper 4. Loopers are in general use between the finishing stands of all mills. The looper shown in Fig. 1 comprises a double arm 5 which carries an idler roller 6 at its outer or down mill end. The arm is pivotally mounted slightly below the level of the mill table and arranged so that it may be tilted up under the strip so as to take up any slack that may occur between successive stands owing to inexact proportioning of mill drafts and speeds of the successive stands. The roller 6 is raised above the -normal pass line by means of a piston 'i which is sldably mounted within the cylinder 8. As shown, the cylinder is pivotally mounted on uprights 9 to provide for slight variations of the connecting rod from a vertical position. To raise the looper roll, the

As used heretofore, the purpose of the looper was to remove slack from the strip.' The presence of slack in a hot strip is dangerous bel cause the strip may fold over to a triple thickness and go through the rolls. rence may break the mill rolls, or cause the motor driving that stand to be greatly overloaded.

It is desirable to measure and indicate the tension in the strip without interfering with the normal functioning of the looper to take upslack in the strip. It is therefore an 1mportant obiect of this invention to make use of the looper for its normal function of slack control and to combine with it additional apparatus and indicating devices for obtaining a measurement of tension in the strip. It is desirable that the apparatus and devices to be combined with the looper shall be of such character that they may be used upon loopers already installed and in service.

With the rolls 6 raised above the pass line and the strip I deflected from the pass line to the positions illustrated in dotted lines, the tension in the strip is directly proportional to the downward force on the tension roll and inversely proportional to the height of the roll above the normal pass line for the distance usually used, i. e.

Since H is proportionall to sine a in which a is the angle of rotation of the arm 5 from its normal position,

T` Sine a in which k2=a constant determined by k1 and the effective length of the looper arm.

In order to measure and indicate the tension T, means are provided for producing two voltages of which one is proportional to the downward force on the roll and the other is proportional to sine a. l

'he means for producing thevoltage proportional to the downwardiorce on the roller comprises a reactance bridge circuit of which the reactance coils II and I2 constitute the ratio arms, the reactance coil ISa of the fixed air gap reactor constitutes the third arm and the coil Ila of the variable air gap reactor Il constitutes the balance arm or fourth arm. The reactor Il is mounted in a sealed casing IIb and is provided with a diaphragm Ilo of magnetic material. A conduit I5 provides communication between the space beneath the piston in cylinder 8 and the interior of the casing IIb. Consequently the pressure `exerted. lagainst the lower face of the piston is also exerted against the upper -face of the diaphragm and deflects it from its normal horizontal position by an amount proportional to the pressure as indicated by the dotted line. When the roller 6 is at rest in any position, the downward pressure of the strip against the roller is equal to the upward pressure of the roller against the stripwhich is proportional to the of the reactor I4 is of such value that the bridge -is balancedand zero voltage appears across theoutput terminals I2a and Md.

A deflection of the diaphragm I4c from its normal unstressed position varies the reluctance of the magnetic circuit of the reactor and thereby varies the reactance of its winding Ia. This unbalances the bridge and ycauses an alternating voltage to appear across the output terminals which is proportional to the unbalance and is therefore lproportional to the vertical pressure on the tension roller. This alternating voltage is rectified by suitable means such as the biphase full wave rectifier I8.U The rectified voltage which is also proportional to the downward pressure on the tension roller appears across the output terminals I8a and Ib of the r'ectiiier.

v The means'for producing a voltage proportional to the sine of angle a. comprises a rotary induction device I9 such as the device known as a selsyn. This device has a. stator member (not shown) upon which is wound a three element distributed winding ISa which is physically similar to the three phase winding of a, wound rotor induction motor, and a rotor member (not shown) upon which is mounted a single element winding I9b in inductive -relationship with the three element winding. Two of the winding elements I9a, are supplied from the single phase alternating voltage source IB, I1. f

When the angle between the longitudinal axis of the single elementr winding ISb and the axis of the magnetic field produced by the winding lila is 90 degrees, zero voltage is induced in the windpressure exerted against the lower face of the Thisvoltage is supplied to a stationary coil 2Ia of an electric ratio meter 2|. Similarly, the voltage which is proportional to the downward presysure on the tension roller is supplied to a second stationary winding 2lb of the ratio meter.` Preferably, the ratio meter is a magnetic vane repulsion type of instrument. As shown this instrument has a stationary magnetic vane 2Ic which extends'longitudinally of the coil 2Ia and a movable vane 2Id which also extends longitudinally of ther coil. Both vanes are magnetized by the flux of the coil. The ends of the vanes which are seen in the drawing have the same polarity, and the opposite ends have the opposite polarity. Thus, when the coil the vanes are magnetized the vanes repel each other, which causes the movable vane to move.

Similarly, the coil 2Ib has a stationary vane 2Ie and a movable vane 2I,f. The'two movable vanes 2Id and 2If are mounted on a common shaft 2Ig. At its upper end the shaft carries a needle 2Ih which moves over a graduated scale 2li. The instrument has no springs and thus the movablek vanes are unbiased.

When both coils are energized the movable vanes assume positions with respect to their cooperating stationary vanes such that the deection of the needle 2Ih from one of its end limiting positions is proportional to the ratio of the iluxes of the two coils 2Ia and 2lb and therefore proportional to the ratio of the downward pressure on the tension roller and the sine oi the angle a, i. e., its deflection is proportional to sine a Since the tension in the strip is also proportional to P sinea the scale 2H of the meter may be calibrated in terms of pounds tension in the strip.

The apparatus in the modification of Fig. 2 is identical with the apparatus of Fig. 1 with the l exception that the diaphragm type pressure reing If9b. As the winding I9bis rotatedfrom this which sponsive reactor I4 of Fig. 1 is replaced by a strain gage 22 which is connected between oneend of the piston connecting rod 23 and thelooper arm 2| which carries the tension roller 25. An enlargement of the strain gage is shown in Fig. 3. It comprises a piece of metal 26 of suitable dimensions, which is placed under compression by the force exerted by the piston. Within its elastic limit it is shortened in proportion to such compression. Fastened near the opposite ends of the compression member are parts 21 and 29 of the magnetic core of a variable reactor. .A coil 21a is wound on the central leg of the core part 21. It is connected as one leg of a bridge which is identical with the bridge of Fig. 1.

The` gap between the two core parts is decreased as the compression of the member 22 is increased. This varies the air gapA and .the reluctance of the magnetic circuit, therebyvarying the reactance of the coil 21a and unbalanc-` ing the bridge circuit just as. deflectionfof, the

unbalansjhe bridgeis energized `and I torque'motor Il, to the drive shaft'pi which the arm Il is connected throughl reduction gearing 32 and $3. The armature of the motor Il is connected in a loop circuit with the armature oan adjustable voltage generator Il. This generator is driven at a speedwhich is substantially constant by suitable means. such as the induction motor Il, which is supplied from a suitable source. such as represented by the three supply lines 38. The motor Iiand generator I4 areprovided with ileld windings lia and Ila respectively which are supplied from a suitable source as indicated in the drawing.

A torque motor is essentially the same as a conventional motor, but it is designed to have sumcient ventilation to enable it to be operated under stalled condition without damage to its winding. Thus. in operation the motor Il rotates the a'rm 2l until its torque is balanced by the downward pressure of` the strip against the tension roller. The motor stalls but exerts a continuous torque on the arm 20. A resistor 3l is included in the armature circuit oi' the motor. It limits the current to a safe value.

It is .assumed that theexcitation of the eld winding ci the torque motor is constant. Consequently the torque oi the motor is proportional to the armaturev current.

A voltage proportional to the armature current is obtained from a voltageI drop resistor 3l which is included in the armature circuit. Since the armature current is proportional to torque of the motor and the downward pressure of the strip on the tension roller II, the voltage drop across the resistor Il is also proportional to the downward pressure of the strip on the pressure roller. This voltage is supplied to one oi' the coils of the ratio meter j ust as the voltage from the bridge'is supplied to the coll 2lb of the ratio meter oi' Fig. 1.

The remainder of the apparatus is identical with corresponding elements of Fig. 1, and a repetition of the description of .these elements and theirI operation is omitted.

'Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it ls now contemplated applying that principle, it will be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modications will readily suggest themselves to persons skilled in the art without departing from the true spirit oithis invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A combined looper and tensiometer fori measuring tension in a strip oi' material extending between two adjacent work performing devices, comprising a tensioning roller disposed to bear-against the strip, a pivoted arm supporting said roller, means for applying a force to said arm to rotate said arm through an angle to defleet the strip from the line between said work devices, means responsive to said rotation for producing a voltage proportional to the sine of said angle, means rponsive to said force for producing a voltage proportional to said force,

and an electrical ratio meter ratio of said voltages.

2. A combined looper and tensiometer for measuring the tension in a strip of material extending between two adjacent work performing devices comprising a tensioning roller disposed to bear against the strip, a pivoted arm supporting said roller, means for applying a force to said arm to rotate said arm through an angle to deect the strip from the line betweensaid work Vdevices comprising a cylinder, a piston in said cylinder connected to said arm and means for supplying pressure duid to said cylinder, means responsive to said rotation for producing a voltage proportional to the sine of said angle, means:

responsive to said force for producing a voltage proportional to said force comprising an electrical pressure gauge responsive to the pressure in said cylinder.' and an electrical ratio meter for measuring the ratio of said voltages.

3. A combined looper and tensiometer for measuring the tension in a strip of material extending between two work performing devices comprising a tensioning roller disposed to bear against the strip, a pivoted arm supporting said roller, means for applying a force to said arm to rotate said arm through an angle to deflect the strip from the line between said work devices, means responsive to said rotation for producing a voltage proportional to the sine of said angle comprising a rotary induction device having primary and secondary winding elements and a mechanical connection between one of i said elements and said arm for eiecting relative movement of said elements in response to rotation of said arm, means responsive to said force for producing a voltage proportional to said force, and an electrical ratio meter for measuring the ratio of said voltages. 4

4. A combined loo'per and tensiometer for measuring tension in a strip of material extending between two adjacent work performing devices. comprising a tensioning roller disposed to bear against the strip, a pivoted arm supporting said roller. means forapplying aforce to said arm to rotate said arm through an angle to deilect the strip from the line between said work devices, means responsive to said rotation for producing a voltage proportional to the sine of said angle, means responsive to said force for vproducing a voltage proportional to said force comprising a Wheatstone bridge, a variable gap reactance device having a winding connected as an arm of said bridge and diaphragm responsive to the pressure of said pressure iiuid for varying the reactance of said winding,

5. A combined looper and tensiometer for measuring tension in a strip of ymaterial extending between two adjacent work performing devices. comprising a tensioning roller disposed to bear .against the strip, a pivoted arm supporting said roller, means for applying a force to said arm to rotate said varm .through an angle to deect the strip from the line between said work devices. means responsive to said rotation for producing a voltage proportional to the sine of said angle, means responsive to said force for 4producing a voltage proportional to said force comprising a strain gauge responsive' to said force. and an electrical ratio meter for .measurl ing the ratio of said voltages.

6. A combined looper 'and tensiometer for measuring the tension in a 4strip of material extending between two workperforming devices comprising a tensioning roller disposed to bear for measuring the" 7 8 against the strip, a pivoted arm supporting said roller, an electric torque motor for rotating said REFERENCES CITED 4arm through an angle t0 deflect the strip from The following references are of record in the the line between said work devices, means reme of this patent: sponsive to said rotation for producing a voit- 5 age proportional to the sine of said angle. means UNITED STATES PATENTS responsive to the armature current of said Number Name Date motor for producing a voltage proportional t0 2,323,818 ussmann Julyfe, 1943 the force of Said roller against the Strip. and all 2,340,067 Lessmann Jan. 25, 1944 electrical ratio meter for measuring bhe ratio 0f l0 2,343,229 stone Feb. 29, 1944 vvsaid voltages. 2,353,249 I .ebourgI July 11, 1044 JAMES D. CAMPBELL. n 2,426,390 De Forest Aug. 2s. 1947 

